Ultrahigh-strength steels at elevated temperatures

Lassi Keränen,Matti Kangaspuoskari,Juhani Niskanen

doi:10.1016/j.jcsr.2021.106739

Lassi Keränen, Matti Kangaspuoskari + Show 1 more

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https://doi.org/10.1016/j.jcsr.2021.106739

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Abstract

The main purpose of this research is to bring deeper understanding about the use of compression loaded ultrahigh-strength steel components at elevated operating temperatures. Another reason for this research is lack of design guidelines concerning ultrahigh-strength steels. This paper provides elevated temperature tensile test data for S700 and S960 ultrahigh-strength steels and discusses the implications of the data from the point of view of structural engineering based on Eurocode 3 design procedures. The experimental part of this paper consists of the tensile testing of two ultrahigh-strength steels grades at temperatures between room temperature and 1000 °C. The models for predicting the temperature reduction factors of Young's modulus, yield strength, ultimate strength and proportional limit are also proposed based on the test results. The obtained proportional limit values together with calculations exhibited that the capacities against buckling of S700 and S960 steels at elevated temperatures are weaker than assumed in Eurocode 3 and Tetmajer's theory for these steel grades. This is mainly due to the lower proportional limit values at room temperature than expected. However, the detected proportional limits do not decrease as fast as Eurocode 3 assumes while the operating temperature increases.

Highlights

During recent years, the upper limit of the strength range of commercially available structural steels has increased considerably [1]
The steel grades S960 and S700 have been investigated and key material parameters needed for EC3 design procedures were determined as a function of temperature for the test temperatures 20, 200, 400, 600, 800 and 1000 °C
- The measured proportional limits were lower than Tetmajer's theory assumes, but the proportional limits do not decrease so quickly than Tetmajer's theory and Eurocode 3 assumes, while the operating temperature increases

Summary

Introduction

The upper limit of the strength range of commercially available structural steels has increased considerably [1]. This development has not been accompanied by developments in design rules, recommendations, engineering knowledge and fabrication experience regarding ultrahigh-strength steels. Due to the lack of design guidelines, the use of the ultrahigh-strength steels with yield strengths over 700 MPa is, uncommon, especially in civil engineering. Farahi et al [3] have examined the capacity of compression loaded concrete-filled double-skin tubular (CFDST) sections, where the corner tubes were fabricated of mild and ultrahighstrength steels (yield strengths 1247 and 305 MPa).

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